1. Field of the Invention
The present invention relates to a long magnetic sensor for detecting a magnetic pattern which is printed on, for instance, paper money.
2. Description of the Related Art
Magnetic sensors for distinguishing, for example, paper money and securities on which predetermined patterns are printed using magnetic inks are disclosed in Japanese Patent No. 2921262 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2003-107142 (Patent Document 2). A configuration of the long magnetic sensor disclosed in Patent Document 1 is shown in FIGS. 8A and 8B. FIG. 8A is a plan view showing magnetosensitive portions with a cover being removed. In this example, magnetic resistance elements (MR elements) 2a to 2e are provided with pairs of magnetosensitive portions 20a to 20e, respectively. The magnetic resistance elements 2a to 2e are aligned and fixed in a case 1. A detection object is arranged in a direction that is perpendicular to the longitudinal direction of such a long magnetic sensor 200.
FIGS. 9A and 9B are front elevation views showing a structure of the lower portions of the magnetic resistance elements, and the state of magnetic fields which are applied to the magnetic resistance elements. Note that only three magnetic resistance elements 2b to 2d are shown here. Magnets 5b to 5d are disposed at lower portions of the magnetic resistance elements 2b to 2d so that magnetic fluxes pass through the magnetic resistance elements 2b to 2d perpendicularly.
FIG. 9B shows the state where magnetic substances (magnetic inks) 101c, 101cd, and 101d of the detection object are in the vicinity of the long magnetic sensor. The magnetic substances 101c, 101cd, and 101d reach the vicinity of the long magnetic sensor sequentially with a time-lag. When the magnetic substances 101c, 101cd, and 101d are present within the magnetic fields produced by the magnets 5c and 5d, concentration of the magnetic fluxes is induced to the magnetic substances, and the magnetic flux density of the magnetic fluxes passing through the magnetosensitive portions 20c and 20d is increased. This causes an increase in the resistances of the magnetic resistance elements, and thus, the presence of the magnetic substances 101c, 101cd, and 101d is detected.
However, many of the magnetic fluxes headed toward the magnetic substance 101cd, which are located at the central portions of the two adjacent magnetosensitive portions 20c and 20d, do not pass through the magnetosensitive portions 20c and 20d, but rather, pass through a gap Gh formed therebetween. Since changes in the magnetic flux density of the magnetic fluxes passing through the gap Gh do not alter a magnetic resistance effect due to the magnetosensitive portions 20c and 20d, a detection level (detection capability) in the vicinity of the gap Gh is degraded. FIG. 8B shows exemplary characteristics of the detection level with respect to locations in the longitudinal direction of the long magnetic sensor.
However, the long magnetic sensor including the location where the detection level is degraded as shown in FIG. 8B is inappropriate when it is necessary to detect the magnetic substance pattern extending over the detection object. To solve this problem, as disclosed in Patent Document 2, a configuration is provided in which magnets and magnetic resistance elements are disposed in a zigzag arrangement, respectively, in a plane parallel to the magnetosensitive portions of the magnetic resistance elements.
FIG. 10A shows a configuration of such a long magnetic sensor. FIG. 10A is a plan view showing the magnetosensitive portions with the cover being removed. In this example, the magnetic resistance elements 2a to 2g are disposed in the case 1 in a staggered, zigzag manner in a plane parallel to the magnetosensitive portions. A detection object is arranged in a direction that is perpendicular to the longitudinal direction of the long magnetic sensor 200.
As described above, the arrangement of the plurality of magnetic resistance elements 2a to 2g in a zigzag manner ensures a substantially uniform detection level over the longitudinal direction of the long magnetic sensor as shown in the exemplary characteristics shown in FIG. 10B.
However, as shown in FIG. 10A, in the long magnetic sensor in which the magnetic resistance elements are disposed in a zigzag manner in a plane parallel to the magnetosensitive portions, the locations of the two adjacent magnetic resistance elements may be deviated from each other by a gap Gv in a moving direction of the detection object. Accordingly, additional signal processing or data processing is required for correcting a time-lag corresponding to the positional deviation of Gv. In addition, since a correction amount of the positional deviation between the adjacent magnetic resistance elements may be different from that between other adjacent magnetic resistance elements depending on the accuracy of the moving speed of the detection object, it is difficult to provide a uniform output.
Furthermore, while the detection object is moved between the case of the long magnetic sensor and a conveying roller, if a distance between the magnetosensitive portions and the detection object is varied in a path between lines Lf and Lb as shown in FIG. 10A, the detection level may also be varied. Accordingly, it is also difficult to properly adjust the distance between the conveying roller and the long magnetic sensor.